The steps to replicate this issue are as follows:
Create a new user (from Odoo "Users" menu)
Set the new user's password (which can be anything, apparently)
Delete that new user.
The error I got was
Integrity Error
The operation cannot be completed, probably due to the following:
- deletion: you may be trying to delete a record while other records still reference it
- creation/update: a mandatory field is not correctly set
[object with reference: Change Password Wizard User - change.password.user]
From what I Googled, it seems that the reason is because the "change.password.user" table (the actual database table name is "change_password_user") still contains a reference to the user I'm trying to delete. But why is that so? And how to fix this problem? Should I manually delete the entry in change.password.user table?